Solutions of organopolysiloxane fluids (silicone fluids) generally containing organic solvents together with relatively small quantities of organo-metallic curing catalysts are used as coating compositions for textiles, paper and similar cellulosic substances and are also useful as encapsulants in the electronics industry for integrated circuits and other electronic devices. Generally, the formulation is applied to the substrate material and the solvent is evaporated therefrom. Upon evaporation of the solvent the catalyst causes the silicone fluid to cure to form a thermoset, high molecular weight, relatively insoluble polymer.
As taught in U.S. Pat. No. 3,575,917, solutions of organopolysiloxanes and curing catalysts in organic solvents have been relatively unstable. The useful life of such compositions has been usually less than one day and often only a few hours and sometimes less even at room temperature. The reason for this limited life is that the curing catalyst causes the organopolysiloxane to cure or condense with itself generally forming a gel-like material or a higher molecular weight more insoluble polymer which cannot be worked or stirred. With the particular materials employed in the present invention, in the absence of a gelation inhibitor, the polymer would so polymerize, forming a gel which would relax if left overnight at room temperature. After relaxation a viscous solution remains. However, the time necessary for relaxation makes mixing and continued use of the polymer impossible until relaxation occurs.
In view of the foregoing, it would be desirable to prepare solutions of the suitable organopolysiloxanes and curing catalysts in organic solvents which can remain stable whereby gelation is inhibited until ready for use. Furthermore, if the particular formulation is to be used as an encapsulant in the electronics industry, the formulation must be devoid of materials which would attack any part of the electronic circuit being encapsulated.